libcxx/include/__memory/temporary_buffer.h

   1 // -*- C++ -*-
   2 //===----------------------------------------------------------------------===//
   3 //
   4 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   5 // See https://llvm.org/LICENSE.txt for license information.
   6 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   7 //
   8 //===----------------------------------------------------------------------===//
   9
  10 #ifndef _LIBCPP___MEMORY_TEMPORARY_BUFFER_H
  11 #define _LIBCPP___MEMORY_TEMPORARY_BUFFER_H
  12
  13 #include <__config>
  14 #include <__type_traits/alignment_of.h>
  15 #include <__utility/pair.h>
  16 #include <cstddef>
  17 #include <new>
  18
  19 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
  20 #  pragma GCC system_header
  21 #endif
  22
  23 _LIBCPP_BEGIN_NAMESPACE_STD
  24
  25 template <class _Tp>
  26 _LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI _LIBCPP_NO_CFI _LIBCPP_DEPRECATED_IN_CXX17
  27 pair<_Tp*, ptrdiff_t>
  28 get_temporary_buffer(ptrdiff_t __n) _NOEXCEPT
  29 {
  30     pair<_Tp*, ptrdiff_t> __r(0, 0);
  31     const ptrdiff_t __m = (~ptrdiff_t(0) ^
  32                            ptrdiff_t(ptrdiff_t(1) << (sizeof(ptrdiff_t) * __CHAR_BIT__ - 1)))
  33                            / sizeof(_Tp);
  34     if (__n > __m)
  35         __n = __m;
  36     while (__n > 0)
  37     {
  38 #if !defined(_LIBCPP_HAS_NO_ALIGNED_ALLOCATION)
  39     if (__is_overaligned_for_new(_LIBCPP_ALIGNOF(_Tp)))
  40         {
  41             align_val_t __al = align_val_t(_LIBCPP_ALIGNOF(_Tp));
  42             __r.first = static_cast<_Tp*>(::operator new(
  43                 __n * sizeof(_Tp), __al, nothrow));
  44         } else {
  45             __r.first = static_cast<_Tp*>(::operator new(
  46                 __n * sizeof(_Tp), nothrow));
  47         }
  48 #else
  49     if (__is_overaligned_for_new(_LIBCPP_ALIGNOF(_Tp)))
  50         {
  51             // Since aligned operator new is unavailable, return an empty
  52             // buffer rather than one with invalid alignment.
  53             return __r;
  54         }
  55
  56         __r.first = static_cast<_Tp*>(::operator new(__n * sizeof(_Tp), nothrow));
  57 #endif
  58
  59         if (__r.first)
  60         {
  61             __r.second = __n;
  62             break;
  63         }
  64         __n /= 2;
  65     }
  66     return __r;
  67 }
  68
  69 template <class _Tp>
  70 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_DEPRECATED_IN_CXX17
  71 void return_temporary_buffer(_Tp* __p) _NOEXCEPT
  72 {
  73   _VSTD::__libcpp_deallocate_unsized((void*)__p, _LIBCPP_ALIGNOF(_Tp));
  74 }
  75
  76 struct __return_temporary_buffer
  77 {
  78 _LIBCPP_SUPPRESS_DEPRECATED_PUSH
  79     template <class _Tp>
  80     _LIBCPP_INLINE_VISIBILITY void operator()(_Tp* __p) const {_VSTD::return_temporary_buffer(__p);}
  81 _LIBCPP_SUPPRESS_DEPRECATED_POP
  82 };
  83
  84 _LIBCPP_END_NAMESPACE_STD
  85
  86 #endif // _LIBCPP___MEMORY_TEMPORARY_BUFFER_H